This invention relates to an engine control and more particularly to an improved engine feed back control for a direct injected, internal combustion engine having a catalyst in its exhaust system.
In spite of the advantages of two cycle engines over four cycle engines in regard to complexity and high specific output, the environmental concerns are causing reappraisal of the continued use of two cycle engines. Specifically, the overlap between the scavenge port and exhaust port opening and closing gives rise to the possibility that unburned hydrocarbons may pass into the atmosphere through the exhaust port.
It has been thought that the performance of these engines can be improved by utilizing such methodologies as feedback control and/or direct cylinder fuel injection in order to improve their performance and make their continued use more feasible.
With feedback control systems, an engine combustion condition sensor such as an oxygen sensor is positioned in proximity to the combustion chamber or the exhaust system so as to sense the oxygen content of the exhaust gases at the completion of the burning cycle. By determining the amount of oxygen present, it is possible to tell if the engine is running rich or lean. Then, feedback control is possible to maintain the desired fuel/air ratio and, accordingly, improve the exhaust emission control.
Direct cylinder injection also is useful in improving engine performance. With direct cylinder injection, the amount of fuel injected per cycle can be more accurately controlled and this is particularly important with two cycle engines.
In addition to the use of feedback control and direct cylinder injection, it may also be necessary or desirable at times to employ a catalyst in the exhaust system for such engine. The catalyst is capable at times of removing constituents that are difficult to remove in other manners or may be a more economically feasible way of treating the exhaust gases.
However, it is known that catalysts operate at fairly high temperatures and this can be a particular problem with marine applications and particularly in outboard motors. Therefore, it is desirable to ensure that the catalyst does not become overheated in its operation even if the feedback control system is operating normally and properly.
It is, therefore, a principal object of this invention to provide an improved feedback control system for a two-cycle engine embodying a catalytic exhaust treatment in addition.
It is a further object of this invention to provide an improved fuel injection control system of the feedback type for a two-cycle marine propulsion engine.